Java Binary Tree. Printing InOrder traversal

Question

I am having some problems printing an inOrder traversal of my binary tree. Even after inserting many items into the tree it's only printing 3 items.

public class BinaryTree {

    private TreeNode root;
    private int size;

    public BinaryTree(){
        this.size = 0;
    }

    public boolean insert(TreeNode node){

        if( root == null)
            root = node;

        else{
            TreeNode parent = null;
            TreeNode current = root;
            while( current != null){
                if( node.getData().getValue().compareTo(current.getData().getValue()) <0){
                    parent = current;
                    current = current.getLeft();
                }
                else if( node.getData().getValue().compareTo(current.getData().getValue()) >0){
                    parent = current;
                    current = current.getRight();
                }
                else
                    return false;

                if(node.getData().getValue().compareTo(parent.getData().getValue()) < 0)
                    parent.setLeft(node);
                else
                    parent.setRight(node);
                }
            }
            size++;
            return true;
        }


    /**
     * 
     */
    public void inOrder(){
        inOrder(root);
    }

    private void inOrder(TreeNode root){
        if( root.getLeft() !=null)
            this.inOrder(root.getLeft());
        System.out.println(root.getData().getValue());

        if( root.getRight() != null)
            this.inOrder(root.getRight());
    }



}

i guess you can call it hw. i'm having a test on binary trees and inOrder traversal might be one of the questions. i'm just trying to brush up on things. — user69514, Apr 24 '10 at 21:23
I highly suggest you don't have a method that takes in a parameter 'root' when the class also has a field 'root'. This makes things very confusing. — Justin Ardini, Apr 24 '10 at 21:24
Following Justin's comment, I think you should make inOrder(..) a static method. It has nothing to do with the specific tree instance. Actually the inOrder method body seems fine. You should check your insertions maybe. — Eyal Schneider, Apr 24 '10 at 21:28

score 1 · Answer 1 · answered Apr 24 '10 at 21:36

You insert method has a problem. It finds the right parent node to attach the new element to, but on the way it messes up the whole tree. You should move the insertion code out of the while loop:

public boolean insert(TreeNode node){

    if( root == null)
        root = node;

    else{
        TreeNode parent = null;
        TreeNode current = root;
        while( current != null){
            if( node.getData().getValue().compareTo(current.getData().getValue()) <0){
                parent = current;
                current = current.getLeft();
            }
            else if( node.getData().getValue().compareTo(current.getData().getValue()) >0){
                parent = current;
                current = current.getRight();
            }
            else
                return false;
        }

        if(node.getData().getValue().compareTo(parent.getData().getValue()) < 0)
            parent.setLeft(node);
        else
            parent.setRight(node);
        }

        size++;
        return true;
    }
}

score 1 · Accepted Answer · answered Apr 24 '10 at 21:38

It seems that you are not traversing the tree properly upon insertion, to find the right place for the new node. Right now you are always inserting at one child of the root, because the insertion code is inside the while loop - it should be after it:

public boolean insert(TreeNode node){

    if( root == null)
        root = node;

    else{
        TreeNode parent = null;
        TreeNode current = root;
        while( current != null){
            if( node.getData().getValue().compareTo(current.getData().getValue()) <0){
                parent = current;
                current = current.getLeft();
            }
            else if( node.getData().getValue().compareTo(current.getData().getValue()) >0){
                parent = current;
                current = current.getRight();
            }
            else
                return false;
        }
        if(node.getData().getValue().compareTo(parent.getData().getValue()) < 0)
            parent.setLeft(node);
        else
            parent.setRight(node);
        }

        size++;
        return true;
    }

score 0 · Answer 3 · answered Mar 12 '17 at 04:27

hey fellows here is one simple one.. try this out.. it works for me well...

public void levelOrderTraversal(Node root){
    Queue<Node> queue = new ArrayDeque<Node>();
    if(root == null) {
        return;
    }
    Node tempNode = root;
    while(tempNode != null) {
        System.out.print(tempNode.data + " ");

        if(tempNode.left != null)   queue.add(tempNode.left);
        if(tempNode.right != null)   queue.add(tempNode.right);

        tempNode = queue.poll();
    }
}

Java Binary Tree. Printing InOrder traversal

3 Answers3